Stereophonic receiving system



Dec. 20, 1949 K. DE BOER ET AL 2,491,9I &

STEREOPHONIC RECEIVING SYSTEM Filed July 2, 1946 V fig. 1.

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Application July 2, 1946, SerialNo. 680,894 In the Netherlands March 19,1943 Section 1, Public Law 690, August 8, 1946 Patent expires March 19,1963 6 Claims.

This invention relates to a receiver for sound images which are takenstereophonically and transmitted separately and which are suppliedthrough at least partly separated receiving channels to reproducingdevices that are separated in space.

For transmitting stereophonically taken sound images at least twotransmitting channels are required. The transmission by means of twotransmitting channels may, for instance, take place by modulating andtransmitting the two sound images on diiierent carrier waves. When for astereophonic transmission, two different carrier waves are notavailable, the two side bands of a single carrier wave may be utilizedto constitute transmitting channels. In principle satisfactorystereophcnic transmission is possible in either way.

Due to fading, however, the overall gain of the transmission channels,which may be defined as being the ratio between the signal strength onreception and that on transmission, is generally not the same for thetwo sound images.

If, however, the overall gain for the two sound images is not equal,distortion of the resulting sound image occurs.

The invention is based on the recognition that a normal automaticamplification control of the receiving channels is not sufiicient toavoid this distortion.

According to the invention, a control oscillation is transmitted witheach sound image and the amplification of at least one Of the receivingchannels is controlled automatically, in accordance with the intensitydiiierences of the control oscillations, in such a manner that theinfluence of differences in the overall gain for the two sound images onthe reproduced resulting sound image is eliminated at least for thegreater part.

When the transmission of the sound images takes place through differentcarrier waves any of them may act as a control oscillation. If, incontradistinction thereto, a single carrier wave is used for thetransmission of the two sideban-ds of one carrier wave, at least oneadditional oscillation must be emitted as a control oscillation. In thiscase preferably two control oscillations are added which are located oneither side of the carrier wave.

The receiver is preferably designed in such a manner that each of thereceiving channels is controlled in the aforesaid manner. Furthermore itis advisable that the amplification of at leastv one of the receivingchannels of the resound images.

ceiver should also be controlled in accordance with the intensity of theincoming associated control oscillation. Excellent results are obtainedby controlling the amplification of one or more stages in at least oneof the receiving channels in accordance with the intensity of theincoming associated control oscillation, the amplification of one ormore of the next stages being controlled in accordance with theintensity differences of the control oscillation-s.

Instead of control in accordance with the receiving intensity of theassociated control oscillation, the amplification of at least one of thereceiving channels may also be controlled automatically in accordancewith the average intensity of the two incoming control oscillations.

In this case the amplification of one or more stages in at least one ofthe receiving channels is preferably controlled in accordance with theaverage intensity of the incoming control oscillations, theamplification of one or more of the next stages being controlled inaccordance with the intensity differences of the control oscillations. Avery simple receiver is obtained by rectifying each of the incoming andamplified control oscillations by means of a single rectifier and by socombining the rectified control oscillations as to obtain at least twocontrol voltages appropriate for automatic control. The value of one ofthese control voltages depends on the intensity differences of thecontrol oscillations and that of the other control voltage depends onthe average intensity of the incoming oscillations.

In order that the invention may be clearly 1111- derstood and readilycarried into effect it will now be described more fully with referenceto the accompanying drawing, given by way of example.

In Fig. l a receiver according to the invention is representedschematically. The receiver is designed for receiving a transmission inwhich two stereophonically taken sound images are transmitted. Thistransmission takes place separately. The receiver comprises tworeceiving channels each of which amplifies and reproduces one of the Thetwo sound images are transmitted on different carrier waves which act atthe same time as control oscillations for the auto matic amplificationcontrol. The oscillations picked up by an antenna are first ofall-amplified by high-frequency amplifiers I0, 20,then-frequency-transformed in mixing stages II, 2|; and subsequentlyamplified again in intermediatefrequency amplifiers I2, 22 and I3, 23. 5

After that the oscillations are detected in rectifiers i4, 24, amplifiedin low-frequency amplifiers I5, 25 and reproduced by loudspeakers I6,26.

which is a measure of the intensity of the incoming associatedcarrier-wave, the amplification of the amplifiers l0, l2 and 2G, 22respectively is controlled, as indicated by arrows in the figure. Fromthe rectifiers I4, 24 is taken a control voltage which is a measure ofthedifference in receiving intensity of, the two carrier waves. By meansof this control voltage the amplification of the intermediate frequencyamplifiers I3, 23 is controlled in such a manner that the amplificationof the receiving channelhaving the smaller carrier-wave amplitude isincreased and that of the other channel is decreased. It is notnecessary first of all to derive from the rectified signals a controlvoltage that is a measure of the intensity difference of the two carrierwaves. As an alternative theoutput voltage of the rectifier Hi may besupplied to the amplifier 23 and the output voltage of the rectifier 24to another amplifier, e. g. the amplifier 22. In this way a differentialcontrol can be established without first producing a differentialcontrol voltage.

In the drawing the differential control is indicated by arrows. Inpractice it has been found that thiscontrol permits a satisfactorystereophonic reproduction in spite of fading.

A still better result is obtained by means of the receiver schematicallyrepresented in Fig. 2. This receiver is difierent from that shown inFig. 1 in that the rectifiers IT and 21 are missing and furthermore inthat there is only one set of intermediate-frequency amplifiers i2, 22.

The control voltages are now directly taken from the rectifiers hi, 2d.One control voltage controls automatically the amplification of thehigh-frequency amplifiers It, 2i] in accordance with the averageintensity of the two incoming control oscillations. The other controlvoltages provide for the differential control of the amplifiers I2, 22in such a manner that the amplification of the receiving channel havingthe smaller control oscillation is increased and that of the channelhaving the larger control oscillation is reduced. In the drawing the twocontrols are indicated by arrows.

In Fig. 3 a diagram of a receiver shown in Fig. 2 is further elaborated.

In this event the two high-frequency amplifiers and the two mixingstages are jointly designated H3 20 The intermediate-frequencyamplifiers i2, 22 are coupled with the rectifiers I4, 24 throughintermediate-frequency band-pass filters I8, 28. The output voltages ofthese rectifiers are set up across series-connected resistances 30, 3|and 40, 4| respectively, the junction of the two resistances 30, 3| and43, H being earthed. By combining the voltages set up across theseresistances different control voltages can be obtained.

Thus, for instance, a potentiometer consisting of two-series-connectedresistances I9, 29 and being connected to corresponding ends of theresistances 39, 419 permits the obtainment of a control voltage whichdepends on the average intensity of the incoming control oscillations.By means of this control voltage the two highfrequency amplifiers I andare controlled; this control is indicated by arrows in the drawing. Thecontrol voltages for the difierential control are obtained byconnectingtwo potentiometers consisting of resistances 32, I2 and 33, 43respectively each to opposite ends of the resistances 3|, and 30, 43respectively. The control voltag taken from the potentiometer 32, 42 issupplied through a resistance 44 to the control grid of the intermediatefrequency amplifier 22, whereas a control voltage taken from thepotentiometer 33, 43 is supplied through a resistance 34 to the controlgrid of the intermediate-frequency amplifier l2.

The low-frequency oscillations are supplied I through resistances 35, 45to the low-frequency amplifiers I5, 25 and reproduced by loudspeakersI6, 26.

The circuit shown in Fig. 3 has the advantage 'over that shown in Fig. 1in that each incoming carrier wave requires only one amplifier; of, thetwo rectifiers required in total the difierent control voltages and, asthe case may be, the lowfrequency oscillations to be reproduced may betaken.

' What we claim is:

In a stereophonic sound receiving system having stereophonic sound imagecomponents in I a given intensity ratio relative to each other, firstamplification channel means, means to apply a first stereophonic soundimage component and a first control oscillation having an intensityproportional to the intensity of said first sound image component tosaid channel means, second amplification channel means, means to apply asecond stereophonic sound image component and a second controloscillation having an intensity proportional to the intensity of saidsecond sound image component to said second channel means, first andsecond spatially separated sound reproducing means coupled to said firstand second channel means respectively, and means responsive to thedifference in intensity of said control oscillations to vary theamplification of said channels relative to each other in a sense toapply said first and second sound image components to said soundreproducing means in said given intensity ratio.

2.'In a stereophonic sound receiving system having stereophonic soundcomponents in a given intensity ratio relative to each other, firstamplification channel means, means to apply a first stereophonic soundimage component and a first control oscillation having an intensityproportional to the intensity of said first sound image component tosaid channel means, second amplification channel means, means to apply asecond stereophonic sound image component and a. second controloscillation having an intensity proportional to the intensity of saidsecond sound image component to said second channel means, first andsecond spatially separated sound reproducing means coupled to said firstand second channel means respectively, means to vary the amplificationof said first channel means inversely proportional to the intensity ofsaid first control oscillation, and means responsive to the differencein intensity of said control oscillations to vary the amplification ofsaid channels relative to each other in a sense to apply said first andsecond sound image components to said sound reproducin means in saidgiven intensity ratio.

3. In a stereophonic sound receiving system having stereophonic soundimage components in agiven intensity ratio relative to each other, firstchannel means comprising first and second amplifying stages, means toapply a first stereophonic. sound image component and a first con troloscillation having an intensity proportional to the intensity of saidfirst sound image component to said channel means, second channel means,means to apply a second stereophonic sound image component and a secondcontrol oscillation having an intensity proportional to the intensity ofsaid second sound image component to said second channel means, firstand second spatially separated sound reproducing means coupled to saidfirst and second channel means respectively, means coupled to said first5 channel means to vary the amplification of said first amplifying stageinversely proportional to the intensity or said first controloscillation, and means responsive to the difference in intensity of saidcontrol oscillations to vary the amplifica tion of said secondamplifying stage in a sense to apply said first and second sound imagecomponents to said sound reproducing means in said given intensityratio.

4. In a stereophonic sound receiving system having stereophonic soundimage components in a given intensity ratio relative to each other,first amplification channel means, means to apply a first stereophonicsound image component and a first control oscillation having anintensity proportional to the intensity of said first sound imagecomponent to said channel means, second amplification channel means,means to apply a second sterecphonic sound image component and a sec--ond control oscillation having an intensity proportional to theintensity of said second sound image component to said second channelmeans, first and second spatially separated sound reproducing meanscoupled to said first and second channel means respectively, meanscoupled to said first and second channel means to vary the amplificationof said first channel means inversely proportional to the averageintensity of said control oscillations, and means responsive to thediiference in intensity of said control oscillations to vary theamplification of said channels relative to each other in a sense toapply said first and second sound image components to said soundreproducing means in said given intensity ratio.

5. In a stereophonic sound receiving system having stereophonic soundimage components in a given intensity ratio relative to each other,first channel means comprising first and second amplifying stages, meansto apply a first stereophonic sound image component and a first controloscillation having an intensity proportional to the intensity of saidfirst sound image component to said channel means, second channel meanscomprising third and fourth amplifying stages, means to apply a secondstereophonic sound image component and a second control oscillationhaving an intensity proportional to the intensity of said second soundimage component to said second channel means, first and second spatiallyseparated sound reproducing means coupled to said first and secondchannel means respectively, means coupled to said first channel means tovary the amplification of said first amplifying stage inverselyproportional to the intensity of said first control oscillation, meanscoupled to said second channel means to vary the amplification of saidthird amplifying stage inversely proportional to the intensity of saidsecond control oscillation, and means responsive to the diiference inintensity of said control oscillations to vary the amplification of saidsecond and fourth amplifying stages in a sense to apply said first andsecond sound image components to said sound reproducing means in saidgiven intensity ratio.

6. In a stereophonic sound receiving system having sound imagecomponents in a given intensity ratio relative to each other, firstchannel means comprising first and second amplifying stages, means toapply a first stereophonic sound image component and a first controloscillation having an intensity proportional to the intensity of saidfirst sound image component to said channel means, second channel meanscomprising third and fourth amplifying stages, means to apply a secondstereophonic sound image component and a second control oscillationhaving an intensity proportional to the intensity of said second soundimage component to said second channel means, first and second spatiallyseparated sound reproducing means coupled to said first and secondchannel means respectively, means to produce a first control voltageproportional to the average intensity of said first and second controloscillations, means to apply said control voltage to said first andthird amplifying stages, means to produce second and third controlvoltages proportional to the intensity difference between said first andsecond control oscillations, means to apply said second control voltageto said second amplifying stage, and means to apply said third controlvoltage to said fourth amplifying stage, said second and third controlvoltages being applied to said second and fourth amplifying stages in asense to apply said first and second sound image components to saidsoitind reproducing means in said given intensity re 10.

KORNELIS ns BOER. ROELOF VERMEULEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,641,431 Horton Sept. 6, 19271,854,247 Brand et a] Apr. 19, 1932 1,914,103 Bjornson June 13, 19331,922,059 Ohl Aug. 15, 1933 1,940,097 Ohl Dec. 19, 1933 2,004,107Goldsmith June 11, 1935 2,004,126 Moore June 11, 1935 2,027,022 ConklinJan. 7, 1936 2,305,917 Beers Dec. 22, 1942 2,352,696 De Boer et al July4, 11944

